1. Field of the Invention
This invention relates to a system for testing the open system interconnect (“OSI”) protocol suit applicable to components that form the physical layer of the OSI model. Instructions within non-proprietary test languages can be sent into a non-proprietary test access port (“TAP”) such as that described in IEEE Std. 1149.1, for testing the serializer and deserializer functions of the physical layer interface at the normal operating speed at which the serial data stream is produced from the serializer and received by the deserializer.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
A communication network typically includes two or more devices which can communicate with each other. The devices are ones which can send digital data. Included with such information are data files, programs, images, etc. An example of such a device may be a network switch. Network switches distribute data across the network, regardless of whether the network is a local area network or a wide area network.
There are numerous ways in which a network switch can interface with the network. The OSI protocol suite attempts to describe the numerous protocols that are employed within the various layers of the OSI reference model. The OSI model is known to include seven layers, where the lowest layer known as the physical layer includes the various protocols and hardware needed to interface a device, such as a network switch, to the other hardware elements which form the network. The physical layer thereby assists in describing the various ways in which a network switch can link to dissimilar network conductors. For example, the network conductor can be coaxial cable, typically found in an Ethernet environment; optical fiber, typically found in fiber-distributed data interface (FDDI); or the well-known token ring and X.25 environments. Each type of link within the network can be designed to receive its own specific protocol. For example, the well-known IEEE 802.3 represents the Ethernet protocol for sending information across an Ethernet coaxial cable.
The physical layer, therefore, represents an interface or “bridge” between a bus to the internal switch circuitry of a network switch and the network transmission line (e.g., optical fiber, coaxial cable, wireless, twisted pair, etc.). In order to interface a bus containing data (e.g., a local bus) of the network switch to, for example, a coaxial cable destined to transfer Ethernet protocols, the physical layer interface must be capable of transferring parallel-fed information on the bus to serialized information on the network during a transmit operation, and to receive serial information from the network and present parallel-fed information back to the bus during a receive operation. Moreover, the physical link layer must also be capable of operating at the relatively low transfer rate of the bus and the much higher transfer rate of the network cable, fiber, etc.
The physical layer used to bring about a proper interface is typically contained on a network interface card or a line card. Each network switch has one or more line cards that can be connected to, for example, the network switch motherboard as well as the network link. In some instances, the entire physical layer function of bridging parallel and serial data operating at dissimilar clock speeds can be performed on a single integrated circuit. A popular such circuit includes products available from Cypress Semiconductor Corp., such as CYP15G0402DX and CYS25G0101DX.
While physical devices are, in general, somewhat comprehensive in their functionality, their ability to perform self-test operations of interface functionality is also fairly limited. A problem exists in that the physical device must operate between the range of the network switch bus and the extremely fast transition speeds of, for example, signals sent across an optical fiber. The physical device can, for example, be a single-chip synchronous optical network (SONET) that transfers information according to asynchronous transfer mode (ATM) protocol at transfer rates exceeding 1 GHz. The ATM cells are sent across the physical medium, such as OC-48 optical fiber. OC-48 formats data into a frame 16 pages deep at a transfer rate of 2.488 Gbits/sec. If the bus to which the physical device is connected is a 16-bit parallel bus, then the differences in transfer rate between the bus and the OC-48 optical fiber is 155.5 (i.e., 2.488 Gbits/sec./16) Mbits/sec. and 2.488 Gbits/sec. The relatively large disparity makes testing of the serializer and deserializer functions within the physical device difficult. Only highly sophisticated and very expensive automated test equipment (ATE) can attain test speeds exceeding 1 GHz, and even fewer can attain speeds exceeding 2.4 GHz.
As more and more physical layer devices are integrated, fewer of such devices output their controls to pins on the physical device. Accordingly, even if a high speed ATE system can be deployed, such a system would not be able to send and receive information into the internal control conductors of the physical layer device. For example, many physical layer devices can be deployed as a programmable logic device (PLD). Unlike application specific integrated circuits (ASIC), PLDs embed their functionality and control within a universally programmable circuit that is not easily accessible (for high speed test) outside that circuit. It would, therefore, be desirable to implement a test circuit within the confines of the PLD that can be enabled using a non-proprietary access port. It would be further desirable that the on-board test circuit be able to test physical device functionality at the high speeds attributable to, for example, OC-48 without requiring expensive proprietary ATEs.